Comparison of the effects of menadione and 2,3-dimethylnaphthoquinone on the energy-coupling reactions of beef-heart mitochondria. Evidence for the involvement of a thiol group in the reactions of oxidative phosphorylation

Young, J.M.

Biochemical Pharmacology 20(1): 163-171


ISSN/ISBN: 0006-2952
PMID: 4398313
DOI: 10.1016/0006-2952(71)90482-5
Accession: 042626399

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Incubation of beef-heart mitochondria with 80 μM menadione abolishes the ability of 2,4-dinitrophenol to release state 4 respiration. Incubation with 80 μM 2,3-dimethylnaphthoquinone is without effect. The percentage rotenone-sensitivity of the state 4 respiration in the presence of menadione does not alter appreciably on incubation. In the case of 2,3-dimethylnaphthoquinone there is a slow increase. Immediately following the addition of menadione the state 4 respiration is totally insensitive to cyanide, but becomes about 35 per cent cyanide-sensitive on continued incubation, indicating the presence in tightly-coupled beef-heart mitochondria of a factor which promotes the cyanide-insensitive oxidation of menadiol, but which is itself slowly inactivated. The cyanide-sensitive respiration in the presence of 2,3-dimethylnaphthoquinone remained constant at 35 per cent. These observations are most simply explained if menadione reacts with a thiol group essential for an early reaction of mitochondrial energy-coupling. The failure of menadione to cause any progressive inhibition of the energy-linked reduction of NADP+ by Nadh in submitochondrial particles is consistent with this suggestion.